This invention generally relates to the conduction system of the heart and the creation of artificial lines of conduction in the wall of the heart to reduce or eliminate cardiac dysrhythmias, for example atrial fibrillation and also to conduct normal impulses from the senatorial node to avoid the necessity of implanting an artificial pacemaker.
The conduction system of the normal heart involves impulse formation at the sinus node and impulse propagation through the rest of the heart. Automaticity, or the property of generating spontaneous depolarization to threshold, enables the SA and AV nodes to generate cardiac action potentials without any stimulus. Automaticity is also present in the left atrium and is thought to contribute to the cause of atrial fibrillation.
The SA node sets the pace because normally it has the fastest rate, which is why it is called the natural pacemaker of the heart. The impulse propagates from the SA note to the AV node and from there to the bundle of His (atrioventricular bundle, common bundle) and finally through the bundle branches of the interventricular septum to Purkinje fibers in the heart wall.
Failure of conduction along the pathways can cause various pathologies. A failure of conduction between the sinus node and the atrium will result in the arrhythmia known as SA block. Failure of conduction can also occur at the level of the connection between the atrium and ventricle. This would produce arrhythmias known as AV block. Establishment of a conduction pathway between these sites should prevent these forms of arrhythmias. This invention provides a means and method for creating conduction pathways between these sites to prevent AV and SA block.
Atrial fibrillation may be caused in part by the failure (partly or totally) of conduction from the AV node to the left atrium. This would reduce the regulating effect of the AV node impulse on the left atrium and leave the areas of automaticity in the left atrium to initiate impulses independently of AV regulation, or in competition with residual AV impulses. The establishment of a conduction pathway from the AV node to the left atrium may prevent atrial fibrillation without recourse to ablative surgery and the implantation of artificial pacemakers. This invention provides a method and a means to provide artificial conduction pathways between these sites. This method would address the cause of fibrillation more directly than present methods.
Another approach to treating atrial fibrillation would be to create a network of pathways, for example in a grid pattern, that would in effect short circuit the impulses or isolate them into small areas, before they are able to propagate sufficiently to cause fibrillation. This grid pattern would be imparted into the walls of the fibrillating atria. Another pattern might be an array of spiral patterns that would act as a capacitor and dissipate the unwanted impulses. These spiral patterns could be connected to each other or disconnected or some of both. Interleaved X""s or spider patters might also be effective.
Conduction through the tissue can also be affected by the orientation of cells forming the tissue. The cells favour transmission in a direction that follows the line joining the gap junctions between the cells and this can cause the impulse to travel through the heart muscle at different rates and in diverging directions. If these impulse fronts later merge or xe2x80x9creenterxe2x80x9d, from different directions they cause the tissue fibrillate. The establishment of conduction pathways that would even-out the speed of the impulse front through the heart tissues should reduce fibrillation due to reentry. Angina might also be treated by establishing conduction pathways in the walls of the hears where angina pain is experienced.
What is needed then is a method to create conduction pathways between various parts of the heart. Conduction pathways generally being lines or fields along which or through which conduction is favoured or modified.
The use of carbon as a means of reducing resistance of the skin tissue to electrical impulses by tattooing carbon into the skin tissue for the purpose of attaching diagnostic sensors was described by S. A. Hoenig, P. L. Gildenberg and K. S. Krishna Murthy, Generation of Permanent, Dry, Electrical Contacts by Tatooing Carbon into Skin Tissue, IEEE Transactions on Biomedical Engineering, Vol. BME-25, No. 4, July 1978, Pages 380-382. The carbon with fluid carrier was injected into the skin with a syringe having a standard hollow needle. It was found that this method produced better results that standard reciprocating tattoo electrical appliances.
What has not been appreciated until now is that the hearts conductive system can be selectively modified by impregnating materials that impart particular electrical properties to the tissue. This approach will essentially rewire the heart.
Pathways or fields of conduction can best be created by impregnating the tissue with materials that enhance the particular electrical properties being sought. In most cases what will be sought is greater conduction; but in other cases greater impedance or insulation may be sought.
The location of the pathways that are most beneficial will depend upon the electrophysiology of the particular heart being treated. As three dimensional imaging becomes more refined, the conductance pathways of a heart may be studied in greater detail and more sophisticated strategies developed to alter and improve these preexisting pathways with artificial pathways that are described in this invention.
The artificial conduction pathways that are the subject of this patent can be applied by different methods depending on the location and pattern of the pathways that the surgeon wishes to create. Open heart surgery will give the surgeon the most flexibility in applying the pathways and if open heart surgery is necessary due to the location of the pathways required, a simple syringe will be suitable for most cases. In other cases the paths can be applied with a automated syringe that is described in this patent and forms a part of this invention. This hand-held automated syringe can apply any pattern to the inner or outer surface of the walls of the heart, although in most cases the inner pathways will be created on the inside of the heart. While tattooing instruments exist such as those described in U.S. Pat. No. 5,401,242 of Dr. Harold Yacowitz, the existing systems do not permit real-time adjustments in needle depth, amount of material delivered, or changes in the part of the stroke that material is delivered. The automated syringe that is a preferred embodiment of this invention can produce conductive tracts of varying depth, varying densities of material deposited, all without stopping to adjust the instrument. No other system can do all these things.
If a syringe is used, the pathway of conductive materials can be applied by a number of insertions with concomitant injections of a desired amount of conductive material. This series of injections can form a pathway or field, depending upon what is required at various depths in the tissue. This method would be similar to tattoo methods, except that it is not automated, but allows for more control of the pattern of the pathway and field, its extent and depth at various points. This methods would be used of creating conduction pathways close to the surface of the interior heart walls.
The second method of applying a pathway to the heart tissue would be more direct and involve creating an approximately continuous ribbon of conduction material. This would involve inserting the syringe, usually a relatively long distance, and injecting the conducting material while inserting the needle or withdrawing it, or both. The conductive material can be continuous or discontinuous, depending upon what is required. This would be controlled by the surgeon""s application of the syringe plunger, or activation of a pump. This method typically would be used for establishing a conduction pathway at greater depths than the first method described above; for example, from the Sinoatrial node (SA) to the left atrium. For many operations, a combination of both methods might also be required.
For some operations it might be preferable to enter the heart through the lumens of arteries and veins connected to the heart. These methods are well known to the art. A catheter delivered to the heart by these methods could have a distal end that injects the conducting material into the heart tissue by various means. The simplest method would be a long syringe needle that would extend out of a hole at or near the distal end of the said catheter. The distal end of the said catheter needle can be straight or hooked, depending upon what is required. If straight, it would simply exit out of the distal end of the catheter, the lumen of which encloses the needle. If hooked it could be made of superlastic nitinol that would permit it to be straight in the catheter, but rebound into a curved shape as it exits the hole of the side of the catheter. A straight syringe needle would apply straight ahead injections and the curved syringe needle would apply injections along the side of the longitudinal axis of the distal end of the catheter. A catheter could of course accommodate a number of syringe needles to speed the application of the track or pattern. These could exit, bundled together, out of one hole or out of separate holes. If a curved needle is used, means for aligning the distal needle tip with the hole in the side of the catheter through which it must pass, must be provided. This could be a simple ridge placed longitudinally along the distal portion of the needle that would register with a groove running along the longitudinal axis of the wall of the distal end of the catheter. Other means well known to the art could also be used to align the curving needle to ensure that it exits at the hole properly.
A preferred embodiment of the invention for the delivery of the material is an automated syringe and catheter system. The curved and straight needle could of course be automated and have an automated pump that would pulse at the same time the needle was inserted into the tissue. This would require that the either or both the needle and the interior walls forming the lumen of the catheter be insulated, by for example Teflon. The needle would then change its impedance when it entered the tissue of the heart and material would not be pumped unless the capacitance was such that the needle must be in the tissue. This would prevent material from mixing in with the blood of the heart. This pulse of the pump could be programmed by computer means to also vary the amount of material delivered at each part of the stroke. For example it might be important to have more material ejected at the end of a stroke, while in other cases it might be important to have it ejected evenly from the point of entry to the end of the throw of the needle""s back an forth motion. It is also important to vary the depth stroke of the needle into the tissue. The conduction track required might vary in depth along the interior wall of the heart, it is therefore important to be able to vary the depth that the needle can penetrate. This can be accomplished by controlling the servo motor that drives the needle by computer means. It is also important to know when the needle is about to leave the hole in the distal end of the catheter and when it returns and is fully sheathed by the catheter as well as the length the needle has extended from the hole in the delivery catheter. Again this can be done by providing a series of contact points with a known and different resistances at the distal end of the needle that will make contact with a contact point on the distal end of the delivery catheter. The relative position of the tip of the needle and the hole of the catheter can then be determined by detecting the resistance in the circuit formed by the catheter and needle through the various contact points, such detection takes place outside the body and this information is reported to the computer which controls the motion of the needle and the pump. This will ensure that the needle""s position is known to the computer during the procedure. Other positional detection means are well known to the art, such as linear induction measuring devices, but these are all well known to the art and other preferred embodiment could incorporate these means. Because the needle must be somewhat loose in the lumen of the catheter to permit movement, it is unreliable to measure the relative positions of the distal needle tip and said hole from outside the body. As can be readily appreciated this method of delivery is quite different from that described in U.S. Pat. No. 5,401,242 of Dr. Harold Yacowitz. The computer controlled servo motor and servo pump allow for on-the-fly control of needle stroke, speed of stroke and amount of material deposited at each part of the stroke. These parameters can be varied as the operation is being conducted, even at every stroke of the needle. The tissue insertion detection means also ensures that no material is deposited in the blood stream and also allows for a variation in the separation between the catheter and the heart wall into which the needle in injected.
The preferred material for impregnation are particles or molecules of carbon 60, or other forms of carbon including activated carbon, and other organic materials, such as conductive plastics, that are conductive and that are at the same time biologically compatible with the heart muscle. Other preferred materials are particles of any inorganic conductive material that is biologically compatible, for example iron, stainless steel, nickel titanium (nitinol) and oxides of these metals. However, Carbon 60 is thought to be the best material as it is relatively inert, conductive and has high lubricity which would minimize irritation from the movement of the heart muscle. Other forms of carbon, iron and iron oxide are the principal other preferred materials due to their conductivity and bio-compatability. Radio-opaque dies can be added to the material to be impregnated to allow the surgeon to view the progress of the operation. If these materials are applied with a syringe or similar device, they will be suspended or dissolved in a carrier fluid such as saline water, or other suitable carrier fluid used in other pharmacological preparations.
Rather than injecting carbon materials into the tissue, the tissue itself could be carbonized by the application of photo-thermal energy to the tissue. This preferred embodiment of the invention would involve the delivery of the photo-thermal energy, preferably produced by a laser, delivered directly or particularly in the case of an interluminal operation, down an optical fibre to the area of the heart wall that requires carbonization. An infrared or near infrared laser would probably be best for carbonization, but other frequencies would also be suitable. It may be beneficial to use one laser frequency to produce the holes and another to carbonize the lumen of the hole so formed. In this case a tunable laser might be utilized or two lasers optically linked by means well known to the art. The optical fibre would be of such a diameter and the laser pulses of such energy to produce holes of desired diameter and depth to effect the purpose. In some cases holes would not be required in which case surface and near surface carbonization could be effected by using lower energies. Using this method the electrical impulse of the heart need not travel down the axis of an individual tract or hole, but depending upon the depth of the holes and the arrangement of the array of holes, the electrical impulse could travel normal to the axis of the holes. Additional carbon or conductive material could also be introduced into the holes so created to further increase the conductivity of the heart wall.
Another preferred embodiment would be an optical fibre within the lumen of a catheter, the distal end of the catheter being sufficiently sharp to permit it to be pushed through the heart wall and an opening at or near the distal end, to permit the delivery of photo-thermal energy to the adjoining tissue through which the catheter is advanced or retreated. This catheter could be of the steerable or non-steerable type. A device of this type could be advanced through the walls of the heart, and then the carbonizing laser could be turned on while the optical fibre delivery device is pulled back. This would ensure that the position of the tract is correct before the tract is carbonized.
As referred to above, insulating materials, such insulating plastics or ceramic materials could be injected to increase the resistance of the tissues to the passage of the electrical impulse through the tissue. This approach is similar to the ablative surgery approach where the tissue is imparted with higher resistance by cauterizing the tissue. This method of injecting biologically compatible insulating materials would however be much less traumatic. These tracks would in most cases be the same in direction and orientation as the ablative tracts created by conventional means.
Alternatively materials with a high capacitance might be used. This would act as a capacitor smoothing out the pulse and bringing it below the threshold at which it would cause the heart muscle to fibrillate. Materials of this sort could be made from biologically compatible metals with biologically compatible oxide or insulative surfaces such as a ceramic or plastic. As mentioned above, patterns of conductive materials could also create areas of high capacitance.
All three methods, that is tracts of higher conductance, tracts of insulative barriers and tracts of higher capacitance or a combination of two or more of the following, could all be injected into the heart wall be the means described above.
While the method is described mainly in the context of reducing fibrillation, AV and SA block, it should be appreciated that this method allows one to change the electrical properties of the heart for other purposes. For example, heart pace makers could be made more effective and durable if conductive tattoos were impregnated into the tissue of the heart using the methods described. Using such methods pacemakers might be introduced into the patient""s vascular system, e.g. the femoral vein, percutaneously or by way of a cut-down, advanced therein into the heart and implanted into the heart with electrodes tattooed in the heart walls.